Mechanical extension devices for hydraulic or other props

ABSTRACT

A stilt for use with a pit prop comprising an outer tubular member which at one end receives an end portion of the prop and which contains either a variable number of spacer pieces or a variable height spacer piece, and the tubular member has an entry at its end remote from the prop to enable spacer pieces to be inserted and removed or the variable height spacer piece adjusted, such stilt being provided either at the lower end or upper end of the prop which may be incorporated in a selfadvancing roof support comprising a base, a plurality of such props and a roof-engaging superstructure.

Waited States Patent 91 Groetschel [54] MECHANICAL EXTENSION DEVICES FORHYDRAULIC OR OTHER PROPS [76] Inventor: Karl M. Groetschel,Stolzestrasse 44, Bochum, Germany [22] Filed: May 12, 1970 [21] Appl.No: 36,640

[ 30] Foreign Application Priority Data [58] Field 01 Search...248/346,354 H, 354 R, 354 S, 248/356, 357; 254/92, 98, 100,101, 134, 133.1, DIG.l

.[56] References Cited UNITED STATES PATENTS 1,513,252 10/1924 Lampert..254/133,l

1,479,090 1/1924 Slonecker.... ..254/98 396,321 1/1889 Baird .,..248/354S UX 224,499 2/1880 Williams ..254/98 1 Jan.23,1973

2,925,981 2/1960 Wilson et a1. ..248/354 R FOREIGN PATENTS ORAPPLlCATlONS Primary ExaminerWilliam H. Schultz Attorney-Spencer & Kaye[57] ABSTRACT A stilt for use with a pit prop comprising an outertubular member which at one end receives an end portion of the prop andwhich contains either a variable number of spacer pieces or a variableheight spacer piece, and the tubular member has an entry at its endremote from the prop to enable spacer pieces to be inserted and removedor the variable height spacer piece adjusted, such stilt being providedeither atthe lower end or upper end of the prop which may beincorporated in a self-advancing roof support comprising a base, aplurality of such props and a roof-engaging superstructure.

17 Claims, 11 Drawing Figures PATENTEDJMI 23 I975 SHEET 1 [1F 2 INIEMQRKori Moria Graeme; ,4hdl/V 5 BY ATTORNEYS.

MECHANICAL EXTENSION DEVICES FOR HYDRAULIC OR OTHER PROPS BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to amechanical extension device (herein called a stilt) for, or inassociation with, a hydraulic or other pit prop.

In underground mine workings in which such pit props are used there isconsiderable variation in the floor to roof height when may occur inconsequence of variable seam thickness of the coal or other mineralsubstance being mined, and it frequently occurs that even when using themaximum lift or stroke of the prop, the length of the latter isinsufficient to enable it to perform its proper roof supporting functionat places where the floor to roof height is increased above thatnormally encountered in the working as a whole.

2. Description of the Prior Art In an endeavor to overcome this problemit has been proposed to provide, in association with a pit prop, aone-piece body to be fitted to the lower end of the prop. Thisexpedient, however, has the disadvantage that it provides only one valueof incremental increase of the effective length of the prop and is ofsuch form that it can be secured to, and removed from, the prop onlywith a considerable expenditure of manual effort, and furthermoreconstitutes an encumberance to transport in the mine working owingprincipally to the size of the body. Moreover complications are entailedwhere a plurality of such bodies are provided of respectively differingheights appropriate for use at places presenting respectively differentfioor to roof heights.

There have also be proposals to provide a stilt for assembly with thelower end of a prop comprising a plurality of spacer pieces assembled ina stack beneath the lower end of the prop and pivoted to an upright rodoffset laterally with respect to the prop axis, so that they can beswung about the rod into a position beneath the prop or withdrawn fromsuch position.

The disadvantage, however, of this proposal is the low degree ofstability presented by the stack of spacer pieces. Further, there aredifficulties in applying this proposal to a form of mine roof supportwhich is increasingly being brought into use in place of individual pitprops, namely a self-advancing roof support comprising a base, aplurality of props thereon, and a roofengaging superstructure carried bythe props, and traction means for advancing the support.

Yet another prop extension device that has been proposed forincorporating in a self-advancing roof support as above described is onewhich comprises an externally screw-threaded tubular member closed atits lower end to form a socket for receiving the lower portion of theprop and itself inserted into a further tubular member mounted withinone of the prop housings of the base of the support, a nut memberco-operatively engaged with the external thread of the first saidtubular member resting on the upper end of the second tubular member toprovide, in effect, a supplementary screw jack by means of which theheight of the prop can be varied. In the conditions encountered inunderground mine workings, especially coal mines, this proposal has thedisadvantage that it is exposed to damage by way of dirt and fallingrock impinging on the external screw thread, and also entails relativelyhigh manufacturing cost having regard to the relatively large diameterof the screw thread which must be accurately cut. To obtain adequatestrength the tubular member having the screw thread must have arelatively large external diameter and the second tubular member'must,therefore, be made still larger in diameter, these factors contributingmaterially to the cost of both such components.

SUMMARY OF THE INVENTION The object of the present invention is toprovide a mechanical extension device or stilt for, or in associationwith, a hydraulic or other pit prop whether used singly or as part of aself-advancing roof support, and which is of simple and reliableconstruction and capable of economic manufacture, the stilt alsoproviding good stability and being of compact sturdy form. The presentinvention resides in the provision for, or in association with, ahydraulic or other pit prop of a stilt comprising means defining aninner vertical spacer of variable height, means defining an outercontainer for receiving said spacer in its interior and having a lateralwall surrounding said spacer to provide lateral location or supporttherefore around said spacer, entry means in said lateral wallcompatible with maintainance of said lateral location or support butaffording access to said interior for effecting changes of height ofsaid spacer.

In the preferred form the stilt comprises a tubular member open at oneof its ends to receive one end of an associated prop, said spacer is ofsuch size relatively to the internal cross-sectional dimensionspresented by said tubular member to have only small lateral clearancewith respect to said tubular member, said entry means is situatedadjacent to the other end of said tubular member and is of a heightwhich is small compared with the total length of said tubular member.

The opening in the tubular member may thus be of a height sufficient toadmit of insertion of only one spacer piece at a time into the tubularmember and at positions above the opening the tubular member thuspresents an internal surface providing all round lateral location orsupport to any spacer pieces containedtherein projecting above the upperend of the opening.

The spacer may comprise one or more spacer pieces forming a stack insaid tubular member, the number of spacer pieces determining the heightpresented by the spacer, said entry being of a height sufficient only toadmit of the insertion of one of said spacer pieces at a time, atpositions between said entry and said one end of said tubular member thelatter presenting an internal surface providing lateral location orsupport for any of said spacer pieces contained therein at positionsaround the entire perimeter of each of said spacer pieces.

Although nominally of fixed or constant height, one or more of thespacer pieces may be so formed or constructed as to be collapsible inresponse to the application of a downward load exceeding a predeterminedvalue, for example exceeding the yield load of the associated prop. Thisis an additional safeguard, in that when a prop has contracted to themaximum extent, due to application thereto from the roof of the mineworking of a load exceeding the yield load, damage to the prop andpossibly other relatively expensive components of a self-advancing roofsupport in which such prop may be incorporated are avoided. Thecollapsed spacer piece is a comparatively inexpensive component.

Alternatively, I may utilize in the stilt one or more of the variableheight spacer pieces, each of which may incorporate components which aremovable relatively to each other in an upward direction and adjustingmechanism controlling the relative positions of said components andcapable of bearing the downward load applied to the spacer piece when inuse. A particularly convenient form of adjustment mechanism comprises awedge mechanism which comprises a wedge element having its endspresented laterally of the spacer piece and in this case the tubularmember may be formed to include openings at opposite ends of the wedgeelement respectively, and adjacent to the lower end of the tubularmember through which the wedge element can be driven in one direction orthe other to adjust the height of the spacer piece.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described,by way of example, with reference to the accompanying drawings wherein:

FIG. 1 is a view in front elevation, partly in cross-section, of aportion of a self-advancing roof support incorporating a prop equippedwith one embodiment of stilt in accordance with the invention;

FIG. 2 is a plane view of the parts shown in FIG. 1 with the propremoved;

FIG. 3 is a view in side elevation and partly in crosssection of theparts shown in FIG. 1;

FIG. 4 is a fragmentary view showing only the prop and stilt device ofFIG. 1 to 3 with a plurality of spacer pieces inserted to raise thelevel of the prop;

FIG. 5 is a view in front elevation of one form of spacer piece whichmay be incorporated in a stilt inaccordance with the invention;

FIG. 6 is a view in side elevation of a further form of spacer piece;

FIG. 7 is a plane view of still a further form of spacer piece;

FIG. 8 is a view in side elevation of still a further form of spacerpiece;

FIG. 9 is a fragmentary view in side elevation and partly incross-section of a further embodiment of stilt in accordance with theinvention;

FIG. 10 is a view in side elevation, partly in cross-section, of stilla, further form of spacer piece; and

FIG. 11 is a fragmentary view in side elevation and partly incross-section illustrating a further embodiment .of stilt in accordancewith the invention wherein the stilt is assembled with the upper end ofthe associated prop.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring firstly to theembodiment of stilt shown in FIGS. 1 to 4, the stilt is shown applied toa prop 10 incorporated in a self-advancing roof support which comprisesa base, a plurality of props similar to the prop 10 at positions spacedapart thereon, a superstructure (not shown) carried by the props attheir upper ends for engaging and supporting the roof, and a tractionmeans for advancing the support. Typically each of the props issupported in an upstanding housing 11 on the base and such housingcontains a means for maintaining the prop in an upright position asshown whilst permitting it to be tilted to a controlled extent inresponse to lateral loads applied to the superstructure. These meanscomprise four blocks or bodies 12 of rubber or other elastic materialwhich may each be of elongated form spanning one pair of opposed sidesof the housing 11 which is of square configuration as seen in FIG. 2,one such block or body being arranged on each of four sides of the prop.

The lower part of the housing 11 is secured to, and extends upwardlyfrom, one of the floor-engaging members of the base formed, for example,of laterally spaced box-section bars 13 connected by plates 14, theupper of which has a centering ring 15 receiving and providing laterallocation for the stilt 16 provided in ac cordance with the invention.

The stilt comprises a tubular member 17 which may, and preferably does,project upwardly for some distance above the upper end of the housing 11and is centered by the rubber blocks or bodies 12, as mentioned, at itsupper end and by the ring 15 at the lower end.

The tubular member 17 is of such internal diameter as to receive thelower end portion of the prop 10 as an easy sliding fit but withoutsubstantial lateral clearance. In the interior of the tubular member 17is a spacer which may be formed of one or more spacer pieces 18 whichare inserted between the lower end of the prop l0 and a supportingsurface constituted either by a bottom wall 19 of the tubular member 17(if the latter is closed at its lower end) or possibly by the upperplate 14. In some cases, however, it may be convenient for the tubularmember 17 to be open at its bottom end and for the spacer piece or thelowest of them to rest on the floor of the mine working.

The spacer pieces are of square form as seen in plan (FIG. 2) and ofdimensions such that they are circumscribed by the interior surface ofthe tubular member 17 with only slight lateral clearance, that is to saythe diagonals of the spacer pieces 18 are slightly less then theinternal diameter of the tubular member.

This ensures that each spacer piece is located, that is positioned,laterally more or less precisely by the interior surface of the tubularmember and that when a stack of spacer pieces are utilized the tubularmember provides lateral stability preventing the stack collapsing orbulging in the interior of the tubular member.

Conveniently, but not essentially, the spacer pieces are each of aheight equal, or approximately equal, to the lengths of their sides asviewed in plan (so as to be of cubic form or approximately so). Toenable the spacer pieces to be inserted into, and withdrawn from, thetubular member, the latter is formed adjacent to its lower end with anentry in the form of a generally rectangular opening 20. The opening 20has a height which is only a little greater than the height of eachspacer piece individually, as will be evident more particularly fromFIG. 4, and the width of the opening 20 is a little greater than thecorresponding dimension of each spacer piece, that is the length of theside. The

opening 20 thus occupies only a little more than one quarter of thecircumference of the tubular member and the latter is not seriouslyweakened. Moreover, it will be evident that a spacer piece occupying thelowermost position is located by engagement of at least two of itscorners with the internal surface of the tubular member, and that anyspacer piece which is raised to project above the upper boundary of theopening is located against lateral displacement in all directionsrelative to the axis of the tubular member.

It will, of course, be evident that other shapes of spacer piece may beutilized as viewed in plan, for example rectangular section. In thiscase the width of the opening 20 could be reduced still further, forexample it will be as little as one half the internal diameter of thetubular member.

The spacer piece may be of hollow form and conveniently constituted bypieces cut off from a box-section bar. To enable them conveniently to beinserted and manipulated, lifter members 21 are provided, these being inthe form of rods 22 equipped at their outer ends with handles 23. Thespacer pieces are formed with holes 24 through which the lifter memberscan be passed. Extending from the upper boundary of the opening 20 is anextension opening 25 in the form of a slot having a width-slightlyexceeding the cross-sectional dimensions of the rods 22 of the liftermembers and formed above its lower end at a distance at least equal tothe height of each spacer piece with a lateral branch 26, the lowerboundary of which forms a ledge or shoulder on which the rod of a liftermember can be raised to support the associated spacer piece at anelevated position leaving a vacancy beneath it for the insertion of afurther piece.

The housing 11 of the base of the roof support is formed with asufficiently large opening 27 to enable the lifter members and spacerpieces to be manipulated as required. Conveniently the interspace withinthe housing 11 between this and the tubular member 17 forms a storagechamber for accommodation of spacer pieces, as seen particularly in FIG.1.

At a position diametrically opposite the extension opening 25 a matchingopening may be formed in the tubular member so that, as seenparticularly in FIG. 3, a rod 22 of a lifter member can be supported attwo positions thereby permitting the handle to be released whilst afurther spacer piece is introduced into the vacant space beneath theelevated spacer piece.

' Various alternative forms of spacer piece are illustrated in FIGS. 5to 8 to which reference will now be made The space piece of FIG. 5formed from a piece cut off from box-section bar such as that normallyused for the construction of roof supporting bars includes a stop meansin the form of an upstanding stud, bolt or other projection 28 welded orotherwise secured to the bottom wall and of such length as to afford aclearance space 29 between its upper end and the top wall of the spacerpiece.

When subjected to a predetermined load in excess of that capable ofbeing borne by the narrowest sections 30 of the side walls, collapsewill take place limited by engagement of the top wall with the upper endof the projection 28.

As seen in FIG. 6 -a generally similar spacer piece may be modified byformation of holes 31 through its side walls 30 to provide collapse at apredetermined downward load. This load should be greater than the yieldload of the prop. It may exceed this value by about 50 percent of thevalue of which other components of the prop support are superior in loadbearing capacity to the prop itself. Thus, in the event of the supportbecoming jammed between the roof and floor, the spacer pieces bycollapsing in the manner indicated, that is by permanent deformation orfracture, provide additional security against destruction of relativelycostly components of the support, including the props after the latterhave become fully contracted.

In the further form of spacer piece shown in FIG. 7, upper and lowersquare or rectangular plates 32 are connected by an intermediatecylindrical wall 33 through which holes may be bored as seen at 34 forthe purpose already indicated. A stop means in the form of an upstandingbolt or projection 35 is also provided for operation in a manner similarto the projection 2d. The square or rectangular plates 32 engage theinner surface of the tubular member 17 at their comers in a mannersimilar to that already described to provide lateral location andstability.

It will be evident that each of the forms of spacer piece shown in FIGS.5 to 7 includes a cavity which enables the inner end of a lifter memberto be inserted, this being, for example, the open end of the spacerpiece of FIG. 5, the open end or the holes 31 of the spacer piece ofFIG. 6, and the holes 34 of the spacer piece of FIG. 7.

In FIG. 8 the spacer piece therein depicted is of inverted cup-shape.This form of space piece 40 is in tended to be made of brittle materialwhich becomes fragmented under downward loaded exceeding a predeterminedvalue. The hollow interior 41 provides space for the accommodation ofparts broken off. It is also possible to bring about deliberate fractureof the piece 40, for example by hammering or smashing same through theopening 20 at the particular time at which it is required to release ajammed roof support or prop.

It is contemplated that the spacer pieces of FIGS. 5 to 7 would be madeof a metal capable of plastic deformation to provide the required yield,for example steel, whilst the spacer element shown in FIG. 8 may be madeof a brittle material, either metal or a non-metallic material such asglass or a ceramic material.

Referring now to the alternative embodiment shown in FIG. 9, partscorresponding to those already described are designated by likereference numerals with the prefix I and the preceding description is tobe deemed to apply.

In this embodiment a wedge element 142 is provided for operation betweena lower component 143 of a v spacer piece and an upper component 144thereof, the

latter having an inclined lower face matching the inclined face of thewedge element. A housing 145 slotted to permit of transverse passage ofthe wedge surrounds the lower part of the component 144 which has aflange or head 147 engaging the upper end of the housing 145 when thewedge is knocked out to prevent the inclined face of the upper componentbearing against the horizontal, upwardly presented, face at the upperend of the lower component 143. The tubular member 117 may be formedwith a further opening 146 adjacent to one end of the wedge, the otherend of the wedge being accessible through the opening 120. The opening120 may be of sufficient size to permit of insertion of the spacer pieceeither in assembled form or one component at a time, whereas the opening146 is only large enough to permit of operation of the wedgetherethrough. Alternatively the spacer piece could be inserted throughthe top of the tubular member 117 before insertion of the prop.

A further fonn of spacer piece is illustrated in FIG. 10 designed toyield by a substantial distance in the case of application of downwardload exceeding the predetermined value (corresponding to the yield loadof the associated prop).

In this construction the upper component 247 engages in the interior ofa hollow cage-like or cup-shape lower component 248 provided with acotter means 249. The cotter means may be in the form of a relativelythin plate having lateral projections 250 which rest in holes or slotsin the side walls of the lower component and which are sheared form themain body or central portion of the plate when a load exceeding thepredetermined value is applied. Openings 251 at the lower end of thelower component are provided for removal of any sheared parts in theinterior of the lower component. The cotter means 249 may alternativelybe in the form of a transverse bolt or pin. A flange or head 252 on theupper component will engage the upper edge 253 of the lower component atthe limit of downward travel.

It is contemplated that in cases where a plurality of spacer pieces areused, as is shown, for example, in FIG. 4, these will normally be all ofone kind and of nominally fixed height. However, under certainconditions spacer pieces incorporating means for adjusting the height,for example as shown in FIG. 9, may be combined with those shown inFIGS. 5 to 8 and 10. In this case application to a load exceeding apredetermined value will provide yield by virtue of the permanentdeformation or fragmentation of certain of the spacer pieces whilst theadjustment mechanism may be operated subsequently to release a prop orsupport from a jammed position.

Although the spacer pieces are located laterallyby the internal member Imay provide formations on the spacer pieces which supplement laterallocation. For example, a projection could be provided at the undersideof each spacer piece to engage in a recess formed at the upper side ofthe piece next beneath it. Alternatively the centering or locatingformations could be constituted by vertically inter-engaging parts atthe peripheries of the spacer pieces or loose pins engaging in bores orlike formations.

A further embodiment of the invention is illustrated in FIG. 11 whereinparts corresponding to those previously described are designated by likenumerals of reference with the prefix 3, and the preceding descriptionis to be deemed to apply.

In this embodiment the stilt 316 is assembled with the upper end of anassociated prop 310.

The tubular member 317 has its upper end portion received in a cavity orsocket 360 which is presented downwardly at the underside of one of themembers 361 of a roof-engaging superstructure of a self-advancing roofsupport, the remaining parts, namely the base and traction means, ofwhich are omitted for clarity.

The tubular member 317 is connected to the member 361 by connectingmeans such as one or two links of chains 362, so that if thesuperstructure remains in an elevated position, by virtue of continuedextension of other props of the support when the illustrated prop 310 iscontracted, the tubular member 317 also remains in the raised positionsuspended from the member 361, while the upper end portion of the prop310 descends.

Spacer pieces 318 contained in the tubular member 317 thus descendleaving a free space opposite to the entry 320 which allows additionalspacer pieces to be inserted as required.

For removing spacer pieces the prop 310 can be extended until thetopmost spacer piece is in a position just opposite to the entry 320without being under load, whereupon it can be removed either directly orby means of a tool such as the lifter member already described andillustrated in the embodiment of FIGS. 1 to 4.

Iclaim:

1. A prop stilt comprising:

a. an outer tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions are to receive said prop asa close sliding fit;

b. a plurality of spacer pieces each of a size to be closely enclosed bysaid lateral wall superposed in a stack between said prop and the otherend of said ,tubular member; and entry means in said lateral walladjacent to said other end of said tubular member and of a heightsufficient only to admit of the insertion of said spacer pieces singly,said tubular member being of circular form as viewed in plan, each ofsaid spacer pieces being of non-circular form so selected as to presentat least one transverse dimension less than the intemal diameter of saidtubular member, said entry is of a width less than the internal diameterof said tubular member but greater than said dimension of said spacerpieces the shape of each of said spacer pieces is such that, uponinsertion into said tubular member, said spacer piece will contact sameat a plurality of positions spaced apart angularly about the axis ofsaid tubular member to provide the required lateral location or support.

2. A stilt according to claim 1 wherein each of said spacer pieces is a.of polygonal form as viewed in plan and of dimensions to becircumscribed by the internal surface of said tubular member,

b. presents at least one pair of opposite parallel sides spaced apart bya distance less than the width of said entry in said tubular member.

3. A stilt according to claim 2 wherein each of said spacer pieces is ofsquare form as viewed in plan having a diagonal dimension just less thanthe internal diameter of said tubular member to provide the requisiteworking clearance to prevent jamming of said spacer piece duringinsertion into said tubular member, and to allow movement of said spacerpiece along said tubular member when a stack of said spacer pieces isinserted into said tubular members while preserving lateral stability ofsaid stack.

4. A stilt according to claim 3 wherein said entry in said tubularmember extends circumferentially of said tubular member for a distancejust exceeding one quarter of the circumference of said tubular member.

5. A prop stilt comprising:

a. an outer tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions as to receive said prop asa close sliding fit, said one end of said tubular member is adapted toreceive the lower end of the associated P p;

b. a plurality of spacer pieces each of a size to be closely enclosed bysaid lateral wall superposed in a stack between said prop and the otherend of said tubular member;

c. entry means in said lateral wall adjacent to said other end of saidtubular member and of a height sufficient only to admit of the insertionof said spacer pieces singly; and

. a lifter member having means engageable with that one of said spacerpieces in said tubular member situated opposite said entry to supportsaid spacer piece, and any of said spacer pieces above it, duringmovement of said lifter member from a lowered position to a raisedposition through a distance such as to enable a further spacer piece tobe inserted through said entry beneath said cooperative spacer piece andlifter member, said tubular member having has means defining a ledge tosupport said lifter member in said raised position.

6. A stilt according to claim 5 wherein:

a. said lifter member comprises an elongated rod-like member,

b. each of said spacer pieces is formed with at least one cavity toreceive an end portion of said lifter member,

0. the remainder of said lifter member is adapted to protrude from saidtubular member to an external position enabling it to be lifted to raisethe spacer piece cooperate therewith.

7. A stilt according to claim 6 wherein:

a. said tubular member has an upwardly extending opening leading fromthe upper boundary of said entry,

b. said upwardly extending opening and said lifter member are relativelydimensioned to enable said lifter member to move upwardly in saidopening with a portion of said lifter member disposed in the interior ofsaid tubular member supporting one of said spacer pieces, and a furtherportion of said lifter member protruding externally from said tubularmember.

8. A stilt according to claim 7 wherein said upwardly extending openinghas a lateral boundary having an upwardly presented ledge or shoulder ata position above the upper boundary of said entry by a distance at leastequal to the height of each of said spacer pieces.

9. A stilt according to claim 8 wherein said tubular member has afurther similar upwardly extending opening formed therein at a positionopposite that which extends from the upper boundary of said entrywhereby said lifter member can be supported at diametrically opposedlocations on correspondingly upwardly presented ledges or shoulders ofsaid openings respectively.

10. A prop stilt comprising:

a. an outer tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions as to receive said prop asa close sliding fit;

b. a plurality of spacer pieces each of a size to be closely enclosed bysaid lateral wall superposed in a stack between said prop and the otherend of said tubular member; and

c. entry means in said lateral wall adjacent to said other end of saidtubular member and of a height sufficient only to admit of the insertionof said spacer pieces singly, at least one of said spacer piecesincluding a hollow body having side walls of a thickness selected toestablish vertical collapse of said spacer piece in respect of loadingthereof in a direction longitudinally of said stilt exceeding apredetermined value.

- 11. A stilt according to claim 10 wherein said side walls areapertured to present a cross-sectional area in a horizontalcross-sectional plane such that said side walls will undergo collapse inresponse to application of said predetermined load.

12. A stilt according to claim 10 wherein said hollow body contains stopmeans for limiting the extent of vertical collapse of said body.

13. A prop stilt, comprising:

a. an outer tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions as to receive a prop as aclose sliding fit;

. a plurality of spacer pieces each of size to be closely enclosed bysaid lateral wall superposed in a stack between such prop and the otherend of said tubular member; and

0. entry means in said lateral wall adjacent to said other end of saidtubular member and having a height slightly greater than that of eachspacer piece for permitting the insertion of only one said spacer pieceat a time, and of a width less than any internal cross-sectionaldimension of said tubular member, said spacer pieces each having atleast one dimension which is less than the width of said entry means.

14. A stilt according to claim 13 wherein said tubular member has an endwall at said other end.

15. A stilt according to claim 13 wherein said lateral side wall iscontinuous both circumferentially and axially between said one end and aregion bordering said entry, which region has an axial dimension of thesame order as the height of said entry.

16 A prop stilt comprising:

a. an outer tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions as to receive said prop asa close sliding fit;

b. a plurality of spacer pieces each of a size to be closely enclosed bysaid lateral wall superposed in a stack between said prop and the otherend of said tubular member; and

0. entry means in said lateral wall adjacent to said other end of saidtubular member and of a height sufficient only to admit of the insertionof said spacer pieces singly, said lateral wall being continuous bothcircumferentially and axially between said one end and a regionbordering said entry,

which region has an axial dimension of the same order as the height ofsaid entry, within said region said tubular member having at most'a pairof narrow axially extending slots at diametrically opposed positionseach of a width which is small compared with the dimension of said entrymeasured circumferentially of said tubular member, said slots enabling arod-like lifter to be inserted into and moved axially along the tubularmember for lifting said spacer pieces.

17. A stilt according to claim 13 in combination with

1. A prop stilt comprising: a. an outer tubular member open at one endand having a lateral wall of internal cross-sectional form anddimensions are to receive said prop as a close sliding fit; b. aplurality of spacer pieces each of a size to be closely enclosed by saidlateral wall superposed in a stack between said prop and the other endof said tubular member; and entry means in said lateral wall adjacent tosaid other end of said tubular member and of a height sufficient only toadmit of the insertion of said spacer pieces singly, said tubular memberbeing of circular form as viewed in plan, each of said spacer piecesbeing of non-circular form so selected as to present at least onetransverse dimension less than the internal diameter of said tubularmember, said entry is of a width less than the internal diameter of saidtubular member but greater than said dimension of said spacer pieces theshape of each of said spacer pieces is such that, upon insertion intosaid tubular member, said spacer piece will contact same at a pluralityof positions spaced apart angularly about the axis of said tubularmember to provide the required lateral location or support.
 2. A stiltaccording to claim 1 wherein each of said spacer pieces is a. ofpolygonal form as viewed in plan and of dimensions to be circumscribedby the internal surface of said tubular member, b. presents at least onepair of opposite parallel sides spaced apart by a distance less than thewidth of said entry in said tubular member.
 3. A stilt according toclaim 2 wherein each of said spacer pieces is of square form as viewedin plan having a diagonal dimension just less than the internal diameterof said tubular member to provide the requisite working clearance toprevent jamming of said spacer piece during insertion into said tubularmember, and to allow movement of said spacer piece along said tubularmember when a stack of said spacer pieces is inserted into said tubularmembers while preserving lateral stability of said stack.
 4. A stiltaccording to claim 3 wherein said entry in said tubular member extendscircumferentially of said tubular member for a distance just exceedingone quarter of the circumference of said tubular member.
 5. A prop stiltcomprising: a. an outer tubular member open at one end and having alateral wall of internal cross-sectional form and dimensions as toreceive said prop as a close sliding fit, said one end of said tubularmember is adapted to receive the lower end of the associated prop; b. aplurality of spacer pieces each of a size to be closely enclosed by saidlateral wall superposed in a stack between said prop and the other endof said tubular member; c. entry means in said lateral wall adjacent tosaid other end of said tubular member and of a height sufficient only toadmit of the insertion of said spacer pieces singly; and d. a liftermember having means engageable with that one of said spacer pieces insaid tubular member situated opposite said entry to support said spacerpiece, and any of said spacer pieces above it, during movement of saidlifter member from a lowered position to a raised position through adistance such as to enable a further spacer piece to be inserted throughsaid entry beneath said cooperative spacer piece and lifter member, saidtubular member having has means defining a ledge to support said liftermember in said raised position.
 6. A stilt according to claim 5 wherein:a. said lifter member comprises an elongated rod-like member, b. each ofsaid spacer pieces is formed with at least one cavity to receive an endportion of said lifter member, c. the remainder of said lifter member isadapted to protrude from said tubular member to an external positionenabling it to be lifted to raise the spacer piece cooperate therewith.7. A stilt according to claim 6 wherein: a. said tubular member has anupwardly extending opening leading from the upper boundary of saidentry, b. said upwardly extending opening and said lifter member arerelatively dimensioned to enable said lifter member to move upwardly insaid opening with a portion of said lifter member disposed in theinterior of said tubular member supporting one of said spacer pieces,and a further portion of said lifter member protruding externally fromsaid tubular member.
 8. A stilt according to claim 7 wherein saidupwardly extending opening has a lateral boundary having an upwardlypresented ledge or shoulder at a position above the upper boundary ofsaid entry by a distance at least equal to the height of each of saidspacer pieces.
 9. A stilt according to claim 8 wherein said tubularmember has a further similar upwardly extending opening formed thereinat a position opposite that which extends from the upper boundary ofsaid entry whereby said lifter member can be supported at diametricallyopposed locations on correspondingly upwardly presented ledges orshoulders of said openings respectively.
 10. A prop stilt comprising: a.an outer tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions as to receive said prop asa close sliding fit; b. a plurality of spacer pieces each of a size tobe closely enclosed by said lateral wall superposed in a stack betweensaid prop and the other end of said tubular member; and c. entry meansin said lateral wall adjacent to said other end of said tubular memberand of a height sufficient only to admit of the insertion of said spacerpieces singly, at least one of said spacer pieces including a hollowbody having side walls of a thickness selected to establish verticalcollapse of said spacer piece in respect of loading thereof in adirection longitudinally of said stilt exceeding a predetermined value.11. A stilt according to claim 10 wherein said side walls are aperturedto present a cross-sectional area in a horizontal cross-sectional planesuch that said side walls will undergo collapse in response toapplication of said predetermined load.
 12. A stilt according to claim10 wherein said hollow body contains stop means for limiting the extentof vertical collapse of said body.
 13. A prop stilt, comprising: a. anouter tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions as to receive a prop as aclose sliding fit; b. a plurality of spacer pieces each of size to beclosely enclosed by said lateral wall superposed in a stack between suchprop and the other end of said tubular member; and c. entry means insaid lateral wall adjacent to said other end of said tubular member andhaving a height slightly greater than that of each spacer piece forpermitting the insertion of only one said spacer piece at a time, and ofa width less than any internal cross-sectional dimension of said tubularmember, said spacer pieces each having at least one dimension which isless than the width of said entry means.
 14. A stilt according to claim13 wherein said tubular member has an end wall at said other end.
 15. Astilt according to claim 13 wherein said lateral side wall is continuousboth circumferentially and axially between said one end and a regionbordering said entry, which region has an axial dimension of the sameorder as the height of said entry. 16 A prop stilt comprising: a. anouter tubular member open at one end and having a lateral wall ofinternal cross-sectional form and dimensions as to receive said prop asa close sliding fit; b. a plurality of spacer pieces each of a size tobe closely enclosed by said lateral wall superposed in a stack betweensaid prop and the other end of said tubular member; and c. entry meansin said lateral wall adjacent to said other end of said tubular memberand of a height sufficient only to admit of the insertion of said spacerpieces singly, said lateral wall being continuous both circumferentiallyand axially between said one end and a region bordering said entry,which region has an axial dimension of the same order as the height ofsaid entry, within said region said tubular member having at most a pairof narrow axially extending slots at diametrically opposed positionseach of a width which is small compared with the dimension of said entrymeasured circumferentially of said tubular member, said slots enabling arod-like lifter to be inserted into and moved axially along the tubularmember for lifting said spacer pieces.
 17. A stilt according to claim 13in combination with a prop, said prop having one end portion received insaid tubular member of said stilt with the remainder of said propprojecting from said open end of said tubular member, said tubularmember having internal cross-sectional dimensions such as to receivesaid end portion of said prop as a sliding fit without substantiallateral clearance, and said prop itself including components movablerelatively to extend and contract the prop.